Selected Metals - 4: 400 Series Stainless Steels
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
S400xx (AISI/SAE 400) series are martensitic and steels that are not quite as corrosion resistant as the 300 series. However the non-ferritic varieties will heat treat quite well with ordinary methods. This provides a great deal of utility because the engineer can design machinery that will stand up to caustic cleaning solutions - like that present in food processing plants - yet still have strong hardened machine components. Most 400 series stainless steel is magnetic like carbon steel.

Following are three 400 series stainless steels which the machinist will be familiar: Note how carbon, chromium, and nickel change their properties.

S41600 (AISI/SAE 416 )

  • Carbon 0.08%
  • Chromium 16 to 18%
  • Nickel 10 to 14%
  • Other alloys manganese, sulphur, phosphorus, silicon, molybdenum
  • Machinability easy to machine
  • Hadenability good oil hardening
  • Weldability not recommended
  • Applications shafting, axles, screw machine parts
  • Comments the first free machining stainless.  Widely available

S43100 (AISI/SAE 431)

  • Carbon 0.2%
  • Chromium 15 to 17%
  • Nickel 1.25 to 2.5%
  • Other alloys manganese, sulphur, phosphorus, silicon
  • Machinability galling chips and inferior finishing
  • Hadenability oil or air quenching
  • Weldability arc welding only
  • Applications aircraft fasteners and bolts
  • Comments excellent strength, high hardness levels, best corrosion resistance of any 400 series stainless steel.

S44000 (AISI/SAE 440)

  • Carbon 0.60 to 1.2%
  • Chromium 15 to 17%
  • Nickel none
  • Other alloys manganese, sulphur, phosphorus, silicon, molybdenum
  • Machinability tough stringy chips, use carbide chip breaker, will grind nicely
  • Hadenability good hardening with air or oil quench
  • Weldability do not weld
  • Applications molds, dies, valve components
  • Comments this steel has three sub-parts, 440A, 440B, and 440C, all of which can harden progressively from Rockwell 56 to Rc 60. Poor corrosion resistance.
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